Proceedings of the 39th International Symposium for Archaeometry, Leuven (2012) 171-176

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Swabian and Mamluk gilded and enamelled glass objects: technological affinity through archaeometric investigation.

M. C. Caggiani1°, R. Laviano2, N. Ditaranto1, L.C. Giannossa1, A. Mangone1§, Ph. Colomban3

1. Dipartimento di Chimica, Università degli Studi di Bari “Aldo Moro”, via Orabona 4, 70125 Bari, Italy, maria.caggiani@uniba.it, nicoletta.ditaranto@uniba.it, annarosa.mangone@uniba.it, giannossa@chimica.uniba.it

2. Dipartimento di Scienze della Terra e Geoambientali, Università degli Studi di Bari “Aldo Moro”, via Orabona 4, 70125 Bari, Italy,

rocco.laviano@uniba.it °previously at 3. Laboratoire de Dynamique, Interaction et Réactivité – UMR7075 CNRS, Université Pierre-et-Marie-Curie

(UPMC Univ Paris 06), 4, Place Jussieu, 75252, Paris Cedex 05, France, philippe.colomban@upmc.fr

§Centro Interdipartimentale “Laboratorio di Ricerca per la Diagnostica dei Beni Culturali”, Università degli Studi di Bari “Aldo Moro”, via Orabona 4, 70125 Bari, Italy

ABSTRACT Gilded and enamelled glass objects, coming from a 13th century dump in Melfi’s castle (PZ, Italy), a Frederick II fortress, were investigated. The results were compared with those obtained for Islamic Egyptian and Syrian Mamluk Mosque Lamps (13th-14th century - Department of Islamic Art of Musée du Louvre in Paris) (Colomban et al., 2012). The comparison arose from the resemblance in style of the objects and was carried out with the aim of understanding the links between the Swabian glass and the Eastern models. Both groups were studied by Raman spectroscopy, the Italian samples were also studied by Optical microscopy, Scanning Electron Microscopy and X-Ray Photoelectron Spectroscopy thanks to their fragmentary condition. The bodies of the objects of both groups are comparable (soda-lime-silica glass). As far as enamels and gilding are concerned, similarities in the raw materials and in the technological devices can be highlighted: a hematite and lead-rich red enamel below the gilding, lapis lazuli employed for at least some of the blue enamels and, in some cases, also for the green; calcium phosphate for the white and Naples yellow for the yellow-green ones. Some peculiar features were observed in the Italian samples, such as the exclusive use of cobalt in some of the blue enamels. The archaeological-archaeometric results, which highlight a strong influence of the Eastern production style on the Italian one, lead to the hypothesis that the latter, after an early stage of importation from the Syrian-Palestinian area, became more and more local thanks to the probable presence of skilled Islamic artisans at the court of Frederick II. KEYWORDS Enamel, gilding, glass, spectroscopy, technology.

Introduction Gilded and enamelled glass objects are very precious and attractive; their quality peak was reached in Syria and Egypt under the Ayyubide and then Mamluk dynasties starting from the 13th century (du Pasquier 2007); there were not many Roman precursors, probably less than it is thought, considering the easy confusion between enamelling and simple painting (Brill 2001). The archaeometric studies on objects of this class, provenance and epoch are rare (Freestone & Stapleton 1998, Gueitet al. 2010) and those on earlier materials and/or of different provenance are even less: a study was recently carried out giving an insight into the technology of Roman (first half of the 2nd century) enamelled glass fragments (Greiff & Schuster 2008). In this work we compared two groups of objects, apparently very different in origin but very similar in style, decoration, technique and in some cases shape and presence of inscriptions. The Mamluk artefacts, due to their integrity, fragility and preciousness cannot generally be sampled or moved from the secure rooms of museums. Thus, the recent discovery of large Swabian glass fragments, with very high quality decoration and comparable to the Mamluk ones, offered the opportunity to investigate the production technology of these objects not only with the aim of understanding the level of skill reached at the Swabian court, but also of deepening the knowledge concerning this class of mostly untouchable artefacts. A comparison could be started between the two productions and the respective know-how and skill behind them. Materials and methods The first of the two groups of objects consisted of five masterpieces: one bottle (OA 3365) and four mosque lamps (OA 7352, OA 7880/66, OA 7568, MAO 487a) kept in the Department de l’Islam of Musée du Louvre in Paris. They are assigned to the Mamluk dynasty, that is, to the end of the 13th -14th century with a Syrian/Egyptian provenance. The object decorations are made of blue, red, green, yellow and white enamels plus gildings and show inscriptions with the

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names of sultans or cupbearers or dedications to God (Colomban et al. 2012). The second is a group of glass objects and large fragments coming from Melfi Castle in the South of Italy. In particular they were found in the Marcangione Tower, in a dump dated to the last quarter of the 13th century, when the castle was enlarged and improved by the Angevins after the death of Frederick II. This is a corpus of more than 60 fragments of glasses, bottles, cups and other open and closed shapes; most of them are enamelled (blue, red, green and white enamels) and gilded and show in one case true Arabic calligraphy and in the others pseudo-Cufic decorations; a few fragments have a simple blue transparent trail decoration instead. The Mamluk artefacts could only be studied within the secure rooms of the Louvre Museum deposits (measures preceding the opening of the new Islamic Department). Thus, they were analysed by means of non-destructive Raman spectroscopy through a portable instrument (a HE532 Horiba Jobin-Yvon (France), equipped with a matrix Charge Coupled Device (CCD) detector cooled by Peltier effectat 200K associated with two Laser Quantum Ventus (UK) YAG lasers, lined at 532nm, with a maximum power of 100 or 300mW, Fig.1a). The Swabian fragments, which are of greatest importance for their decoration, shape and degree of integrity, were studied by means of non-destructive Raman micro-spectroscopy (Xplora Horiba Jobin-Yvon (France), YAG 532 and 638 and diode 785nm lasers, equipped with an Olympus (Japan) microscope with a deviator of the laser beam so that it can be focussed on large, intact objects, Fig.1b). Some fragments, samples of the order of a few millimetres in size were taken from the borders in order to minimize the damage on the objects. These could be analysed with different Raman spectrometers and excitation wavelengths: - a Senterra micro-spectrometer Bruker Optics equipped with a Peltier-cooled CCD matrix and with two laser sources: YAG 532nm and diode 785nm; - a HR 800 Horiba Jobin-Yvon equipped with a matrix 256 x 1024 air-cooled CCD detector associated with an Ar+- Kr+ ion laser (wavelengths: 364, 457, 488, 514nm)

These fragments were also subjected to Optical (OM, Carl Zeiss) and Scanning Electron Microscopy, (SEM, EVO-50XVP (LEO)) coupled with Energy Dispersive X-ray Spectroscopy (EDS, Oxford-Link) on cross sections, and X-ray Photoelectron Spectroscopy (XPS, Thermo VG Theta Probe) on the surfaces. Results and discussion Mamluk Objects Glass body As far as the glass constituting the Mamluk lamps and bottle is concerned, the Raman analyses with the portable instrumentation equipped with a green laser could not give high quality spectra on the ancient colourless glass bodies. This is due to the micro-cracks, porosity and deposits which are formed during corrosion and cause a loss before the out-scattering of light. This is clearly shown in Fig.2a in spectra 1 and 2, which are representative of those acquired on the authentic bodies; on the contrary the good quality spectrum 3 was recorded on the foot of one of the lamps. The latter, thanks to the detection of modern pigments in its enamels, proved to be a 19th century restoration. By plotting the maxima of the stretching and bending bands of the glass spectrum, a differentiation of the glass according to the flux can be achieved. In Fig. 3a the areas of distribution of different kinds of glass previously studied are reported (Colomban 2012). Mamluk glass falls in the red circle, close to the soda/soda-lime area. Enamels and gilding Fig.4 shows the representative baseline-subtracted Raman spectra acquired on the enamels of different colours. For the blue colour the signature of radical anions S2

- and S3 was always detected. These are chromophores of minerals from the sodalite group, amongst which lazurite and lapis lazuli are the main minerals. As usual, the green colour was caused by a mixture of blue and yellow pigments; in some cases S2

- and S3- were detected, in others only a lead

antimonate signature was evident. This indicates the probable addition of a cobalt-based raw material to give the green colour in some samples. The cobalt-based material, however, cannot be highlighted with this technique unless a residue of the raw material is present or a precipitation occurs. Red was always obtained using hematite, which can be found both in a lead-rich enamel matrix and in a lead-poor one. White was obtained from calcium phosphate or tin

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Fig. 2. a) Raman spectra of the authentic Mamluk glass (1,2) and of a restored foot (3) acquired with a 532nm laser; b) a representative baseline-subtracted Raman spectrum of Melfi glass bodies acquired with a 364nm laser. oxide. As far as the gilding is concerned, it was always found overlying on a red base; only the doublet of graphitic carbon is detected. It is possible that the combination of the laser beam and of the gold support induces a transformation of disordered carbon into graphite. The presence of carbon could derive from dust or could be indicative of the use of an organic medium for its application. Swabian objects Glass body The glass bodies of the Swabian objects was studied through Raman spectroscopy using a high-energy laser at 364nm. Fig.2b shows a representative spectrum of the glass bodies of the gilded and enamelled fragments studied. Plotting the values of bending and stretching maxima, Swabian glass falls in the blue circle (soda-lime glass). If we zoom into this area (Fig. 3b), we notice the separation between the light blue diamonds, representing the gilded and enamelled glasses, and the squares and triangles representing, respectively, the bodies and decorations of the blue-trailed

fragments. This indicates a slightly different mixture of raw materials.

Fig. 3. a) Plot of the maxima of the stretching and bending bands of Mamluk glass (red circle) and from Melfi (blue circle) over a database (Colomban 2012); b) zoom-in of Melfi samples area. Enamels and gilding On the blue enamels, the green laser revealed the resonance Raman spectrum of S2

- - S3- chromophores (Fig.5, spectrum

1). Spectra 2 to 4 in Fig. 5 are acquired with the use of different wavelengths (458/364nm) in order to highlight the contribution of the glassy matrix, which constitutes the matrix of the enamel rather than that of the pigment. It is interesting to note that these three representative spectra show different maxima of the stretching band with two peaks at circa 970-980 and 1050-1075-1092cm-1, denoting the presence of different types of fluxes in the enamels (Colomban et al. 2006). Spectrum 5, though acquired with a green excitation, does not show any S2

- - S3- signature,

which implies their absence from this enamel. This probably means that cobalt was used instead to give the blue colour.

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Fig. 4. Representative Raman spectra acquired on the enamels of Mamluk samples. Moving to the red coloured enamels, the Raman spectra of the pigment always show the signal of iron oxide in the hematite phase. The spectra, acquired with a UV excitation to highlight the glass signature, appear different according to the analysed spot: this seems to indicate a non-homogeneous matrix with a greater or lower content in lead in different areas. XPS analyses were conducted on the red enamels in order to understand their composition and the role of lead. The analyses were conducted on the cut side of the fragments due to the deep leaching layers present on the surface, as shown in the SEM-BSE microphotograph of a thin section in Fig. 6. In Fig.7a the wide scans of two spots acquired on the red enamel are shown. Apart from the presence of iron oxide in the hematite phase, lead appears to be present into two different oxidation states: as Pb3O4 (the pigment Minium) and as PbSiO3 (Fig. 7b).

Fig. 5. Representative Raman spectra acquired on the blue enamels. 1: S2

-, S3- (532nm); 2-4: glass and S2

-, S3- (364nm);

5: glass (532nm).

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Fig. 6. SEM-BSE microphotograph of a thin section of a red enamel drop with a surface alteration overlying the glass body.

Fig. 7. a) Wide Scan XPS spectra of a red enamel (blue: 20mm spot, red: 100mm spot); b) detailed XPS spectrum of Pb 4f. Concerning the gilding, it is interesting to observe the layer underlying the gilding: as with Mamluk objects, gold is always layered over a red enamel base. XPS analyses were conducted on gold residues on the red enamels: in Fig.8a the blue, wide scan is related to the enamel, the red one to the gold residue. The latter shows two doublets of gold, one, at 84 and 88.1eV is attributed to bulk gold, the other one, with signals at 83.4 and 87.2eV is difficult to attribute (Fig. 8b). It could be assigned to an oxidized form of gold or to the presence of gold nanoparticles (Zhang & Sham 2003). This leads to the suggestion of a use of a colloidal dispersion (Gueitet al. 2010). Comparison As far as the glass bodies are concerned, although Mamluk objects were analysed on the altered surface, which may shift the maxima of the bending and stretching bands, we can say that both classes of materials fall in the field of silica-soda-lime glass.

Fig. 8. a) Wide Scan XPS spectra of a red enamel (in blue) and an overlying gold fragment (in red); b) detailed XPS spectrum of Au 4f. Concerning the enamels, there are strong similarities in the pigments used as raw materials and in the technology employed for their application: lead antimonate (probably pyrochlore solid solution) for yellow and green; hematite for red; calcium phosphate for white and S2

- - S3- (lazurite?) for

blue. These were also found in the blue glazes of pottery coming from sites connected to Frederick II, like Siponto, Lucera, Castel Fiorentino and Castel del Monte (Caselli et al. 2006, Catalano et al. 2007, Clark et al. 1997a, 1997b, Laganara Fabiano et al. 2006, Traini et al 2011), and also in the fragments of the Roman enamelled Lübsow beaker (Greiff & Schuster 2008). Swabian enamels can be distinguished by the presence of cobalt, not only in addition to S2

- - S3-, but also used alone. Also, the absence of

cassiterite in the enamels differentiates the Swabian artefacts. In both groups the glass used to make the enamel is different from that used to make the object, the former being rich in lead. The batch could have been non-homogeneous as a consequence of the use of different recycled matrices and the firing conditions could have prevented their homogenization. Furthermore, the occurrence of leaching in the soil must be taken into account. Conclusions This study, thanks to integrated information, contributed to the better understanding of the production technology of gilded and enamelled glass masterpieces. Strong similarities were shown in the two groups of objects analysed, both in the raw materials used and in the procedures employed to produce them. Although, a few peculiarities do differentiate the Swabian objects. These latter, the missing link between the Norman court importation from the Syrian-Palestinian area and the Angevin local production, were surely produced under a strong influence of Eastern models. They were probably the artwork of skilled Islamic artisans at the court of Frederick II.

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